SOHC.co.uk Forums > CB350/400
Acceptable / normal oil consumption
K2-K6:
"The oil used has therefore a rough life with the result oil changes were a lot more frequent than they are now. This is due in no small measure by synthetic oils being far more resistant to breakdown and shearing forces but the clearances now are in microns, thousands of a millimetre not thousands of an inch which allow modern machines to use 0-30 oils whereas our classics need 10-40 oil which is thicker due to larger ( in comparison) clearances."
This is far more involved a topic than generally appreciated and often projected via internet wisdom.
These Honda engine are, and always have been a 30 viscosity (hot running conditions) engine, with tolerances to match. They've always been far ahead of general motor manufacturer engineering in materials specification and production targets. It's new engines that have caught up with this type of engineering.
Running in ambient temperature below 60degree it's actually a 20 viscosity design because of the clearances of crankshaft main etc and only goes to 30 viscosity because air cooling doesn't have an effect thermostat as does a water cooled engine.
To summarise, it's designed built and produced to a specification that matches modern low viscosity specified modern engines.
Oil life has changed the most not from oil chemistry but accurate fuelling that doesn't dilute the lubricant by passing excess unburnt fuel and combustion byproduct past the piston rings. This is always the reason for change intervals in reality.
Viscosity is not protection in absolute terms, it's just resistance within the system it's being squeezed through by the oil pump pressure. Viscosity is exactly the same in either mineral or synthetic oil when measured against the same criteria, it doesn't differentiate one from the other.
Of those two examples of oil grade above, one does have a higher base oil viscosity than the other. Anyone know which way round that is ?
Lobo:
…you are a mine of information K2-K6; always enjoy / appreciate what you write. Ta.
Cappodimonte:
K2-K6, I don’t intend to get into ‘Oil Wars’ but simply put old engines use thicker oil, if you wish to use synthetics designed for modern engines in old classics, it’s your call.
McCabe-Thiele (Ted):
I have had similar discussions on the Nissan Terrano 4x4 site about the same issues.
The compromise might be the semi-synthetics that are available in similar grades to mineral oils. It's due to the wet clutch that I stay with mineral.
Come back good old Duckhams.
Cappodimonte:
If you want Duckhams Ted, contact Fuzz Townsends Classic oils at Bicester Heritage
They sell all the oils you can think of along with other additives for all sorts of mechanical items.
Been in there a number of times and they are very willing to assist. The whole site is a classic car owners dream, they do have a few motorcycle interests in there too.
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